As auxins are among the most important phytohormones, the regulation of auxin homeostasis is complex. Generally, auxin conjugates, especially IAA glucosides, are predominant at high auxin levels. Previous research on terminal glucosylation focused mainly on the O-position, while IAA-N-glucoside and IAA-Asp-N-glucoside have been neglected since their discovery in 2001. In our study, IAA-Asp-N-glucoside was found to be specifically abundant (as high as 4.13 mg/g) in the seeds of 58 ginkgo cultivars. Furthermore, a novel N-glucosyltransferase, termed GbNGT1, was identified via differential transcriptome analysis and in vitro enzymatic testing. It was found that GbNGT1 could catalyze IAA-Asp and IAA to form their corresponding N-glucosides. The enzyme was demonstrated to possess a specific catalytic capacity toward the N-position of the IAA-amino acid or IAA from 52 substrates. Docking and site-directed mutagenesis of this enzyme confirmed that the E15G mutant could almost completely abolish its N-glucosylation ability toward IAA-Asp and IAA in vitro and in vivo. The IAA modification of GbNGT1 and GbGH3.5 was verified by transient expression assay in Nicotiana benthamiana. The effect of GbNGT1 on IAA distribution promotes root growth in Arabidopsis thaliana.

中文翻译：

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来自银杏的 N-葡萄糖基转移酶 GbNGT1 补充了生长素代谢途径

由于生长素是最重要的植物激素之一，生长素稳态的调节是复杂的。通常，生长素缀合物，尤其是 IAA 葡糖苷，在高生长素水平下占优势。以前关于末端糖基化的研究主要集中在○-位置，而 IAA-ñ-葡萄糖苷和 IAA-Asp-ñ-葡萄糖苷自 2001 年发现以来一直被忽视。在我们的研究中，IAA-Asp-ñ在 58 个银杏品种的种子中发现了特别丰富的葡萄糖苷（高达 4.13 mg/g）。此外，一本小说ñ-葡萄糖基转移酶，称为 GbNGT1，通过差异转录组分析和体外酶测试鉴定。发现GbNGT1可以催化IAA-Asp和IAA形成它们对应的ñ-葡萄糖苷。该酶被证明具有特定的催化能力ñ-来自52个底物的IAA-氨基酸或IAA的位置。这种酶的对接和定点诱变证实 E15G 突变体几乎可以完全消除其ñ-体外和体内对IAA-Asp和IAA的糖基化能力。GbNGT1 和 GbGH3.5 的 IAA 修饰通过瞬时表达测定在本氏烟草. GbNGT1对IAA分布的影响促进根系生长拟南芥.